The initiation of cures of polymeric systems either with peroxides or actinic radiation has long been known to the macromolecular art. Some macromolecules, noteably those containing chlorine, can undergo cure directly with actinic radiation. Irradiation of this type molecule with ultraviolet or violet light causes the chlorine-carbon bond in the molecule to break resulting in loss of chlorine and induction of a free radical on the molecular skelton. Because most of the prepolymers and monomers used when a radiation cure is desired are relatively poor absorbers of radiation in the violet and near ultraviolet regions of the radiation spectrum, it is common to use a radiation cure accelerator. These radiation cure accelerators, which usually up to the present have been relatively low molecular weight compounds, are efficient absorbers of light in the violet and ultraviolet regions. When this radiation is absorbed electrons are promoted to higher energy levels in the molecule. This energy is then transferred to the monomer or prepolymeric oligomers which it is desired to cure. This procedure greatly increases the efficiency of utilization of incident radiation energy and renders the process practical.
The use of these radiation cure accelerators is attended by certain inherent problems. Being relatively low molecular weight compounds, they tend to bleed out of a system in which they are incorporated both before and after cure. This results in lack of shelf stability for materials preformulated for later cure and manifestly is undesirable in the finished product. In addition, while aiding in and initiating cure these compounds do not actually enter into the cure reaction. They remain as low molecular weight inclusions in the cured polymer. Their presence thus reduces the maximum physical properties obtainable in the cured system. Such properties as hardness, abrasion resistance, extensibility and even flexibility are all adversely affected. U.S. Pat. No. 3,661,744 does suggest that the photo cure rate accelerator may be chemically combined with one of the reactive structures in the system to be cured but the illustration given thereof is of a benzophenone combined with a number of monomeric units.
The novel compositions of the present invention provide oligomeric prepolymers which are themselves good absorbers of actinic radiation and which therefore do not require the presence of a separate radiation cure accelerator in the system. These compounds are also relatively high molecular weight radiation cure accelerators which enter into the curing reaction.